Parkinson's disease (PD) is a common neurodegenerative disease caused by progressive loss of mid-brain dopaminergic neurons leading to abnormal motor symptoms such as bradykinesia, rigidity and resting tremor. Many PD patients also experience a variety of non-motor symptoms including cognitive dysfunction, autonomic dysfunction, emotional changes and sleep disruption. The combined motor and non-motor symptoms of Parkinson's disease severely impact patient quality of life.
While the majority of PD cases are idiopathic, there are several genetic determinants such as mutations in SNCA, Parkin, PINK1, DJ-1 and LRRK2. Linkage analysis studies have demonstrated that multiple missense mutations in the Leucine-Rich Repeat Kinase 2 (LRRK2) gene lead to an autosomal late onset form of PD. LRRK2 is a 286 kDa cytoplasmic protein containing kinase and GTPase domains as well as multiple protein-protein interaction domains. See for example, Aasly et al., Annals of Neurology, Vol. 57(5), May 2005, pp. 762-765; Adams et al., Brain, Vol. 128, 2005, pp. 2777-85; Gilks et al., Lancet, Vol. 365, Jan. 29, 2005, pp. 415-416, Nichols et al., Lancet, Vol. 365, Jan. 29, 2005, pp. 410-412, and U. Kumari and E. Tan, FEBS journal 276 (2009) pp. 6455-6463.
In vitro biochemical studies have demonstrated that LRRK2 proteins harboring the PD associated proteins generally confer increased kinase activity and decreased GTP hydrolysis compared to the wild type protein (Guo et al., Experimental Cell Research, Vol, 313, 2007, pp. 3658-3670) thereby suggesting that small molecule LRRK2 kinase inhibitors may be able to block aberrant LRRK2-dependent signaling in PD. In support of this notion, it has been reported that inhibitors of LRRK2 are protective in models of PD (Lee et al., Nature Medicine, Vol 16, 2010, pp. 998-1000).
LRRK2 protein has also been demonstrated to be associated with Lewy bodies, a pathological hallmark of PD as well as other neurodegenerative diseases such as Lewy body dementia (Zhu et al., Molecular Neurodegeneration, Vol 30, 2006, pp. 1-17) thereby suggesting that LRRK2 may be associated with the pathogenesis of these diseases.
A growing body of evidence also suggests a role for LRRK2 in immune cell function in the brain with LRRK2 inhibition demonstrated to attenuate microglial inflammatory responses (Moehle et al., The Journal of Neuroscience Vol 32, 2012, pp. 1602-1611). Neuroinflammation is a hallmark of a number of neurodegenerative diseases such as PD and Alzheimer's disease, thereby suggesting that LRRK2 inhibitors may have utility in the treatment of neuroinflammation in these disorders.
Genome-wide association studies also highlight LRRK2 in the modification of susceptibility to the chronic autoimmune Crohn's disease and leprosy (Zhang et al., The New England Journal of Medicine, Vol 361, 2009, pp. 2609-2618; Umeno et al., Inflammatory Bowel Disease Vol 17, 2011, pp. 2407-2415). LRRK2 is also associated with certain types of cancer, e.g. melanoma as well as renal and thyroid carcinomas (Saunders-Pullman et al., Movement Disorders, Vol 25, 2010, pp. 2536-2541; Looyenga, et al., Proceedings of the National Academy of Sciences, USA, Vol 108, 2011, pp. 1439-1444).
Accordingly, compounds and compositions effective at modulating LRRK2 activity may provide a treatment for neurodegenerative diseases such as Parkinson's disease, Lewy body dementia, neuroinflammation, and for disease such as Crohn's disease, leprosy and cancer.